Refrigeration method

ABSTRACT

AN OPERATION IS MAINTAINED AT A SELECTED LOW TEMPERATURE IS A SYSTEM EMPLOYING A PLURALITY OF REFRIGERANTS BY INDIRECTLY CONTACTING REACTANTS WITH A FIRST LIQUEFIED REFRIGERANT TO REMOVE HEAT FROM SAID OPERATION BY VAPORIZATION OF THE FIRST REFRIGERANT, THE RESULTING VAPORS BEING REMOVED AND CONDENSED FOR REUSE BY INDIRECT CONTACT WITH A CHILLED SECOND REFRIGERANT, THE RESULTING VAPORS BEING RETHAN THE FIRST REFRIGERANT, THE SECOND REFRIGERANT IS COMPRESSED, COOLED AND CHILLED, THE CHILLING BEING ACCOMPLISHED BY INDIRECT CONTACT WITH A CHILLED LIQUID HAVING A BOILING POINT GREATER THAN THAT OF THE SECOND REFRIGERANT. THE COMPRESSED AND CHILLED SECOND REFRIGERANT IS FLASHED TO REDUCE ITS TEMPERATURE FURTHER AND IS THEN EMPLOYED TO INDIRECTLY CONTACT THE FIRST REFRIGERANT TO CONDENSE IT FOR REUSE IN SAID OPERATION.

OC. 12, J M BONEM REFRIGERTION METHD Filed June 5, 1969 PRoPANE coNDeNsERs FIG. H-

coouNG 50 |5\ H20 HIGH STAGE PROPANE H'GH STAGE RECEIVER Lm-nuM BROMIDE CHILLED WATER l cvUNDERs SYSTEM I3 T cooLsR y MAKE-UP :s: i PRoPANE :g: 22;;

i 29. 1` I" 4K 25 I 28h 24 22 .A l2 I PRDPANE 26 Low STAGE 8o cYuNDERs 28? I MAKE-uP I4 250 V WATER ETHYLENE VAPOR FROM REAcToR 31 7 2 ETAx-'Elrfl MA33 `FLASH DRUM ETHYLEME coNoEMsERs FMG. 2 32 35 x 3m I ETHYLENE VAPOR E: Y V

To s2 2;:

f 34 Llouln ETHYLENE '33 y; To REAcToR 37 FROM coNDENsER F361 g 32 POLYMER FROM 37 coALEscme 36- PRoDucT 49 DRUM /48 34 4| T 40 33 'Il vAPoR T032 l f l/ff///l I/ ////////A cATALYsT 47 1 M 33 42 39 PoLvMERlzATIoN FEED 57 DRAIN REAcToR w PuRsED 3?/ 4 ETHYLEME VAPOR I4 l FROM n To 235i mum 54j cmLLED H20 FROM 23 I9 52 PRDPAME vAPoRs FIIGT,

56 --PuRGE DRUM 6.9 INV/MUR 58 JOSEPH M. BONEM V BY TO FLASH DRUM 27 C' NE Y,

ABSTRACT OlF THE DISCLOSURE An operation is maintained at a selected low temperature in a system employing a plurality of refrigerants by indirectly contacting reactants with a first liquefied refrigerant to remove heat from said operation by vaporization of the first refrigerant, the resulting vapors being removed and condensed for reuse by indirect contact with a chilled second refrigerant having a boiling point higher than the first refrigerant; the second refrigerant is compressed, cooled and chilled, the chilling being accomplished by indirect contact with a chilled liquid having a boiling point greater than that of the second refrigerant. The compressed and chilled second refrigerant is flashed to reduce its temperature further and is then employed to indirectly contact the first refrigerant to condense it for reuse in said operation.

BACKGROUND OF THE INVENTION (l) Field of the invention The present invention is directed to maintenance of a selected temperature in an operation conducted at a low temperature. More particularly, the invention is concerned with employing a plurality of refrigerants to maintain a selected low temperature operation such as a polymerization reaction. In its more specific aspects, the invention is concerned with reducing the amount of vapor flashed from a second refrigerant to make available large amounts of the second refrigerant for refrigeration of a first refrigerant which is used in control of temperature in the low temperature operation, the second refrigerant being chilled prior to 'flashing by contact with a chilled liquid having a boiling point greater than the second refrigerant which has a boiling point greater than the first refrigerant.

(2) Description of the prior art It has been known heretofore to use cooled propane to condense ethylene. It has also been known to liquefy methane and/ or natural gas by using various refrigeration systems wherein various combinations of water cooling, expansion, compression and heat exchange have been used.

It is also known to use lithium bromide-water cornbination as a refrigerant-absorbent in an enclosed system. It is also known to separate components of natural gas by use of refrigerants. However, it has not heretofore been taught that an operation involving maintenance of a selected temperature vmay be controlled by employing a plurality of refrigerants each in a closed system wherein the refrigerants have progressively increasing boiling points and wherein -llashing of a chilled second refrigerant is employed to reduce the temperature of the second refrigerant and reduce the amount of vapor flashed making greater amounts of the second refrigerant available for refrigeration of a first refrigerant.

3,011,73 Patented ct. l2, 1971 Prior art considered with respect to the present invention includes the following listed U.S. patents: U.S. 2,541,569, U.S. 2,726,519, U.S. 2,812,646, U.S. 2,896,414, U.S. 2,960,837, U.S. 3,004,919, yU.S\. 3,015,940, U.S. 3,020,- 723, U.S. 3,224,207, U.S. 3,315,477, U.S. 3,408,824.

SUMMARY OF THE INVENTION The present invention may be briefly described and summarized as involving use of a plurality of refrigerants of increasing boiling points to control an operation such as, but not limited thereto, a polymerization reaction in which a first refrigerant is employed to maintain a selected low temperature in the operation by indirect heat eX- change, resulting in vaporization thereof, the vapors of the first refrigerant being condensed to a liquid by indirect heat exchange with a second refrigerant which is compressed, cooled and then chilled by a chilled liquid which has been chilled in a refrigerant-absorption system following which the second refrigerant is flashed to reduce its temperature further, the chilling of the second refrigerant reducing the amount of vapors flashed therefrom and thus increasing the amount of chilled second refrigerant available for condensing the first refrigerant.

BRIEF DESCRIPTION OF THE DRAWING and lighter gases are removed from the second refrigerant, in this case propane.

DESCRIPTION OF THE PREFERRED MODES AND EMBODIMENTS RELATIVE TO THE DRAWING Referring now to FIG. 1 which represents a preferred mode and embodiment, numeral 11 designates the prime mover of a two stage compressor equipped with propane low stage cylinders 14 and high stage propane cylinders 15. Means 12 and 13 represent the mechanical linkage from the prime mover 11 to the cylinders 14 and 15. The cylinders 14 and 15 raise the pressure of propane from about 7 to about 160 p.s.i.g,. The propane in high stage cylinders 1S is discharged therefrom by line 16 into propane condensers 17 wherein the propane is cooled by cooling water introduced by way of line 18. The cooled compressed propane is then discharged by line 19 into the high stage accumulator 60. It is then discharged from accumulator 60 through a cooling means 20 through which cold water circulates by way of lines 21 and 22 from the lithium bromide chilled water system 23; lines 21 and 22 being connected in means 20 by heat transfer surfaces 24 defined by suitable conduits and coils 25 in the lithium bromide chilled water system 23. The chilled propane discharges from means 20 at a temperature within the range from about 40 to about 60 F. by way of line 26 into a flash drum 27 where by reduction of pressure by expansion valve 26a, a portion of the propane is flashed off into line 28 and introduced into line 29 connecting with low stage and high stage cylinders 14 and 15. Make-up propane may be introduced by line 28a controlled by valve 28b.

The propane remaining in flash drum 27 being in a chilled condition has its temperature further reduced by virtue of the ashing operation to a temperature within the range from about to about 30 F. and discharges by line 31 containing an expansion valve 31a into ethylene condensers 32 wherein the chilled propane passes in indirect heat exchange with ethylene vapor, from a polymerization operation, introduced by line 33 and returned to the polymerization operation by line 34. Makeup ethylene may be introduced into line 33 by line 33a controlled by valve 33b. The propane from the ethylene condensers 32 is then returned by line 35 to the low stage cylinders 14 with optional compression as may be desired or required.

Referring now to FIG. 2, the ethylene in line 34 is introduced into heat exchange means 36 in a tubular reactor 37 wherein butyl rubber is being formed from isobutylene and isoprene, feed being introduced by line 38 with catalyst being introduced by line 39. The catalyst may be a solution of aluminum chloride in methyl chloride solvent. Methyl chloride may also be introduced separately or with the feed or with the catalyst. The reactants flow upwardly in polymerization reactor 37 through draft tube 40 and then downwardly through the heat exchange means 36 into which the ethylene liquid is introduced by branch lines 41 and 42 from line 34. The ethylene vapor formed by results of the vaporization of the ethylene to control the reaction in reactor 37 which is removed by line 33 for liquefaction or condensing in condensers 32. Ordinarily, the temperature in reactor 37 may be of the order of from about l40 to about 130 F., but a greater range may be used, the butyl rubber reactor and operation being described as exemplary. Various operations may be conducted at temperatures from about 170 to about +20 F. Circulation is induced in the reactor 37 by an impeller 43 arranged on a shaft 44 in a stuffing box 45 which connects to a prime mover 46.

The ethylene vapor from the polymerization reactor after being compressed by means similar to that shown for compression of the propane vapors in line 33 may contain oil from the compressing means and, therefore, optionally this vapor may be sent by line 33 controlled by valve 47 into a coalescing drum or zone 48 which may also be deemed an oil demister zone. Zone 48 is provided with a filter-type coalescing medium, which is removable, which causes droplets of oil vapors to be formed from the mist or tine oil droplets in the ethyelne vapor. Any coalesced droplets may be drained from zone 48 by line 50 controlled by valve 51 while the vapor substantially free of oil may be returned to the ethylene condensers 32 by line 33 controlled by valve 33a. Valves 47 and 33a allow the zone 49 to be by-passed.

Since the propane employed in the present invention may contain some ethylene vapors, it is desirable to provide for purging the ethylene and/or lighter gases from the propane; therefore, a purge drum 52 provided with an internal heat exchange means 53 may be included in the system. The heat exchange means 53 receives chilled water from lithium bromide chilled water system 23 by way of line 54 with the water being returned thereto by line 55.

Propane from the propane condensers 17 is introduced into the propane high stage receiver 60 by line 19 and propane vapors may be removed therefrom by line 56 and charged into purge drum 52 where the circulation of the chilled water causes liquefaction of the propane with the ethylene vapor remaining in a vaporized condition and is discharged by line 57. The propane from high stage accumulators 60 discharges by line 58 into line 26 which leads into flash drum 27.

The present invention is quite advantageous and useful in that it has resulted in a significant reduction and amount of vapor flashed from chilled propane used in condensing ethylene employed as a refrigerant in a butyl rubber operation.

4 The following table is an illustrative example of the advantages of the present invention.

ILLUSTRATIVE EXAMPLE OF EXPANSION OF BUTYL POLYMERIZATION UNIT REFRIGERATION SYSTEM USING CHILLED WATER It will be seen that for the same amount of propane circulation, reduction of the temperature upstream of a flash drum such as 27 of 42 provided a net temperature change of 26 F. with an accompanying reduction of 40,000 lbs./hr. of propane vaporization rate to effect an enthalpy change of 27 B.t.u./ lb. The compression capacity available 'for the expanded rates was 40,000 lbs/hr. In other words, a considerable advantage in refrigeration was obtained by using chilled water from a lithium bromide chilling system.

In the oil demister zone 49 about 160,000 lbs/hr. of ethylene vapors may be circulated at a p-ressure range from about 300 to about 525 p.s.i.a. with a normal pressure of about 375 p.s.i.a. The temperature in the zone 48 may range from about 30 to 90 F. with the vapor density in lbs./cu. ft. ranging from about 2.06 to` about 3.4, the liquid density lbeing about 45 lbs/cu. ft. The entrainment rate in zone 48 will be from about 100 to 200 lbs. oil/M lbs. ethylene present as fog with the oil droplets in the oil mist having a particle size of 5 microns or lower. With a differential pressure of 1 p.s.i., 98% removal of oil droplets of a particle size of 2 microns or larger are obtained.

In the lithium bromide chilled water system 23, a capacity from about 4 to about 7 h-I B.t.u./hr. transferred to the chilled water may be provided by chilled water circulation which is such that the temperature of the water into the system is 55 F. while the chilled water out of the system 23 is about 45 F. The pressure drop may be about 15 p.s.i.

While the present invention has been described and illustrated with respect to a refrigeration system employed in a polymerization reaction, specically butyl rubber polymerization, the invention is not to be limited thereto but may be used in other operations such as in a Natural Gasoline Plant, Paraxylene Crystallization Unit, Isobutylene Extraction Process, Methyl Ethyl Ketone Dewaxing Process, Ethylene Purification Process, and the like.

The invention is quite advantageous and useful and has been so demonstrated as shown by the data in the table.

The nature and objects of the present invention having been fully described and illustrated and the best modes and embodiments contemplated set forth what I wish to claim as new and useful and secure by Letters Patent is:

1. In a system employing a plurality of refrigerants wherein one of the refrigerants is employed to ma1nta1n an operation by indirect contact at a low temperature, the method which comprises:

maintaining said operation at a selected low temperature by indirect contact of reactants with liquefied ethylene to remove heat from said operation by vaporization of ethylene;

removing ethylene vapor from said operation;

compressing said ethylene vapor;

condensing said compressed ethylene .for reuse in said operation by indirect contact with propane obtained in a subsequent step;

compressing propane after said indirect contact with said ethylene and cooling and condensing said compressed propane;

purging said condensed propane of ethylene vapor by removing propane vapor from the cooled propane and chilling the removed propane vapor by indirect contact with chilled water from a lithium bromide cooling system;

chilling said cooled, condensed and purged propane by indirect contact with chilled water from said lithium bromide cooling system;

dashing said chilled purged propane to reduce further the temperature of same; and

employing said dashed propane to condense said ethylene by indirect contact for reuse in said operation. 2. A method in accordance with claim 1 in which the cooled propane is admixed with the chilled propane before flashing the chilled propane.

3. In a system employing a plurality of refrigerants wherein one of the refrigerants is employed to maintain a polymerization operation by indirect contact at low temperature, the method which comprises:

maintaining said polymerization operation at a selected low temperature by indirect contact of reactants with liquefied ethylene to remove heat from said polymerization operation `by vaporization of ethylene;

removing ethylene vapor from said polymerization operation;

compressing said ethylene vapor whereby said vapor contains a small amount of oil from said compression; contacting said compressed ethylene with a coalescing means in a coalescing zone to remove said oil;

condensing said compressed ethylene for reuse in said operation by indirect contact with propane obtained in a subsequent step;

compressing propane after said indirect contact with said ethylene and cooling and condensing the compressed propane;

removing propane vapor from the condensed propane and purging it of ethylene vapor by chilling the removed propane vapor by indirect contact with chilled water from a lithium bromide cooling system to liquefy the propane vapor and venting ethylene vapor;

chilling said cooled, condensed and purged propane by indirect contact with chilled water from said lithium bromide cooling system;

admixing said liquefied propane with said chilled propane;

flashing said chilled purged propane to reduce further the temperature of same; and

employing said ashed propane to condense said ethylene by indirect contact for reuse in said polymerization operation.

4. A method in accordance with claim 3 in which the polymerization operation is a butyl rubber polymerization operation.

References Cited UNITED STATES PATENTS 2,474,892 7/ 1949 Ecabert `62/--471 X 2,484,875 10/1949 Cooper 62--335 X 2,491,710 12/1949 Calfee et al. 260-85.3 3,478,529 l1/l969l Boykin 62--195 X 3,418,819 12/1968 Grunberg et al 62--40 X OTHER REFERENCES Refrigeration and Air Conditioning, by Jordan, Richard C., and Priester, Gayle B., Englewood Clils, NJ., Prentice-Hall, Inc., 1948, p. 6l.

MEYER PERLIN, Primary Examiner P. D. FERGUSON, Assistant Examiner U.S. Cl. X.R. 

